digitalocean_playbook.yml needs ansible-galaxy module community.digitalocean, general roles need community.docker, install with;
ansible-galaxy collection install community.docker community.digitalocean
Add a DO_API_TOKEN with a digitalocean write API token to your environment variables before running the playbook.
Parameters can be adjusted in group_vars/servers.yml
Note: Due to the way digitalocean charges you for droplets,
each droplet will be minimally charged for one cent,
meaning you'll have to pay droplets * 0.01 cents for each run of the playbook,
with however many droplets you have created and destroyed during the run.